Very low frequency high pass filter

Abstract

A variable frequency module controls a cutoff frequency of a high pass filter and includes a resistive element that communicates with a capacitive element of the high pass filter. A first transistor communicates with the resistive element and a reference node and includes a first source/drain region formed in a first well region and a first diode region formed between the first source/drain region and the first well region. A first node of the first diode region is connected to the first source/drain region and the reference node, and a second node of the first diode region is connected to the reference node.

1. A variable frequency module that controls a cutoff frequency of a high pass filter, comprising:
 a resistive element that communicates with a capacitive element of the high pass filter, and 
 a first transistor that communicates with the resistive element and a reference node and that includes a first source/drain region formed in a first well region and a first diode region formed between the first source/drain region and the first well region, 
 wherein a first node of the first diode region is connected to the first source/drain region and the reference node, and a second node of the first diode region is connected to the reference node. 
 
     
     
       2. The variable frequency module of  claim 1  wherein the first transistor further includes:
 a first contact region formed in the first well region that is connected to the first source/drain region and the first well region. 
 
     
     
       3. The variable frequency module of  claim 2  wherein the first transistor further includes:
 a second diode region formed between a second source/drain region and the first well region, 
 wherein a first node of the second diode region is connected to the second source/drain region, and a second node of the second diode region is connected to the second node of the first diode region and the reference node. 
 
     
     
       4. The variable frequency module of  claim 1 , further comprising:
 a second transistor that communicates with the capacitive element and the reference node, that includes a third source/drain region formed in a second well region and a third diode region formed between the third source/drain region and the second well region, 
 wherein a first node of the third diode region is connected to the third source/drain region and the reference node, and a second node of the third diode region is connected to the reference node. 
 
     
     
       5. The variable frequency module of  claim 4  wherein the second transistor further includes:
 a second contact region formed in the second well region that is connected to the third source/drain region and the second well region. 
 
     
     
       6. The variable frequency module of  claim 5  wherein the second transistor further includes:
 a fourth diode region formed between a fourth source/drain region and the second well region, 
 wherein a first node of the fourth diode region is connected to the fourth source/drain region, and a second node of the fourth diode region is connected to the second node of the third diode region and the reference node. 
 
     
     
       7. The variable frequency module of  claim 4  wherein the first transistor and the second transistor are fabricated via a twin-well process. 
     
     
       8. The variable frequency module of  claim 1  wherein the variable frequency module communicates with a reference voltage. 
     
     
       9. The variable frequency module of  claim 8  wherein the reference node communicates with the reference voltage. 
     
     
       10. The variable frequency module of  claim 1  further comprising:
 an input signal, and
 an output signal, 
 
 wherein a first node of the capacitive element receives the input signal, a second node of the capacitive element communicates with the variable frequency module, and the output signal is generated at the second node of the capacitive element. 
 
     
     
       11. The variable frequency module of  claim 1  wherein the first transistor receives a control signal. 
     
     
       12. The variable frequency module of  claim 4  wherein the second transistor receives a clock signal. 
     
     
       13. A variable frequency module that controls a cutoff frequency of a high pass filter, comprising:
 a resistive element that communicates with a capacitive element of the high pass filter, and 
 a transistor that communicates with the resistive element, wherein the transistor includes a source/drain region formed in a well region, a diode region formed between the source/drain region and the well region, and a contact region formed in the well region, 
 wherein the contact region is connected to the source/drain region, the well region, and a reference voltage. 
 
     
     
       14. The variable frequency module of  claim 13  wherein the resistive element comprises N resistors, and wherein the variable frequency module further comprises N−1 transistors wherein first ends of each of the N resistors are connected together and wherein second ends of each of the N resistors communicates with a respective one of the N−1 transistors and wherein N is an integer greater than or equal to 2. 
     
     
       15. The variable frequency module of  claim 13  further comprising:
 N additional resistive elements that communicate with said capacitive element; 
 N additional transistors that each include a source/drain region formed in a well region, a diode region formed between the source/drain region and the well region, and a contact region formed in the well region, 
 wherein a first end of each of the N additional resistive elements connects to an associated one of the N additional transistors and a second end of each of the N additional resistive elements connects to an adjacent one of the N+1 transistors and wherein N is an integer greater than or equal to 1. 
 
     
     
       16. The variable frequency module of  claim 13  wherein the transistors are NMOS transistors. 
     
     
       17. The variable frequency module of  claim 13  wherein the transistors are PMOS transistors. 
     
     
       18. A variable frequency module that controls a cutoff frequency of a high pass filter, comprising:
 resistive means for communicating with a capacitive means for providing a capacitance of the high pass filter, and 
 first transistor means for communicating with the resistive means and a reference node and that includes a first source/drain region formed in a first well region and a first diode region formed between the first source/drain region and the first well region, 
 wherein a first node of the first diode region is connected to the first source/drain region and the reference node, and a second node of the first diode region is connected to the reference node. 
 
     
     
       19. The variable frequency module of  claim 18  wherein the first transistor means further includes:
 a first contact region formed in the first well region that is connected to the first source/drain region and the first well region. 
 
     
     
       20. The variable frequency module of  claim 19  wherein the first transistor means further includes:
 a second diode region formed between a second source/drain region and the first well region, 
 wherein a first node of the second diode region is connected to the second source/drain region, and a second node of the second diode region is connected to the second node of the first diode region and the reference node. 
 
     
     
       21. The variable frequency module of  claim 18 , further comprising:
 second transistor means for communicating with the capacitive means and the reference node, that includes a third source/drain region formed in a second well region and a third diode region formed between the third source/drain region and the second well region, 
 wherein a first node of the third diode region is connected to the third source/drain region and the reference node, and a second node of the third diode region is connected to the reference node. 
 
     
     
       22. The variable frequency module of  claim 21  wherein the second transistor means further includes:
 a second contact region formed in the second well region that is connected to the third source/drain region and the second well region. 
 
     
     
       23. The variable frequency module of  claim 22  wherein the second transistor means further includes:
 a fourth diode formed between a fourth source/drain region and the second well region, 
 wherein a first node of the fourth diode region is connected to the fourth source/drain region, and a second node of the fourth diode region is connected to the second node of the third diode region and the reference node. 
 
     
     
       24. The variable frequency module of  claim 21  wherein the first transistor means and the second transistor means are fabricated via a twin-well process. 
     
     
       25. The variable frequency module of  claim 18  wherein the variable frequency module communicates with a reference voltage. 
     
     
       26. The variable frequency module of  claim 25  wherein the reference node communicates with the reference voltage. 
     
     
       27. The variable frequency module of  claim 18  further comprising:
 an input signal, and 
 an output signal, 
 wherein a first node of the capacitive means receives the input signal, a second node of the capacitive means communicates with the variable frequency module, and the output signal is generated at the second node of the capacitive means. 
 
     
     
       28. The variable frequency module of  claim 18  wherein the first transistor means receives a control signal. 
     
     
       29. The variable frequency module of  claim 21  wherein the second transistor means receives a clock signal. 
     
     
       30. A variable frequency module that controls a cutoff frequency of a high pass filter, comprising:
 resistive means for communicating with capacitive means for providing a capacitance of the high pass filter, and 
 transistor means for communicating with the resistive means and that includes a source/drain region formed in a well region, a diode region formed between the source/drain region and the well region, and a contact region formed in the well region, wherein the contact region is connected to the source/drain region, the well region, and a reference voltage. 
 
     
     
       31. The variable frequency module of  claim 30  wherein the resistive means comprises N resistor means for providing resistances, and wherein the variable frequency module further comprises N−1 transistor means wherein first ends of each of the N resistor means are connected together and wherein second ends of each of the N resistor means communicates with a respective one of the N−1 transistor means and wherein N is an integer greater than or equal to 2. 
     
     
       32. The variable frequency module of  claim 30  further comprising:
 N additional resistive means for providing resistances; 
 N additional transistor means for controlling current that flows through the N additional resistive means, each of the N additional transistor means including a source/drain region formed in a well region, a diode region formed between the source/drain region and the well region, and a contact region formed in the well region, 
 wherein a first end of each of the N additional resistive means connects to an associated one of the N additional transistor means and a second end of each of the N additional resistive means connects to an adjacent one of the N+1 transistor means and wherein N is an integer greater than or equal to 1. 
 
     
     
       33. The variable frequency module of  claim 30  wherein each of the N+1 transistor means implements an NMOS transistor. 
     
     
       34. The variable frequency module of  claim 30  wherein each of the N+1 transistor means implements a PMOS transistor.